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211.
A. Avella F. Mancini E. Plekhanov 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(3):295-299
By means of the Density Matrix Renormalization Group technique, we have studied the region where XXZ-like behavior is most
likely to emerge within the phase diagram of the F-AF anisotropic extended (J-J’) Heisenberg chain. We have analyzed, in great
detail, the equal-time two-spin correlation functions, both in- and out-of- plane, as functions of the distance (and momentum).
Then, we have extracted, through an accurate fitting procedure, the exponents of the asymptotic power-law decay of the spatial
correlations. We have used the exact solution of XXZ model (J’ = 0) to benchmark our results, which clearly show the expected
agreement. A critical value of J’ has been found where the relevant power-law decay exponent is independent of the in-plane
nearest-neighbor coupling. 相似文献
212.
A cubic spinel conductor CuV2S4, containing the corner-sharing tetrahedral lattice of V, was investigated. Above a structural transition at 90 K, the 51V nuclear spin-relaxation rate 1/T1 is comparatively large in magnitude and tends to saturate at higher temperatures, indicating that the V lattice behaves as a nearly antiferromagnetic metal. By substituting nonmagnetic Sn for V, the susceptibility turns to be of Curie-Weiss type and temperature-independent, suggesting recovery of hidden spins as a result of a partial release of the frustration. These results lead to the conclusion that CuV2S4 is an itinerant-electron frustrated system as YMn2. The CDW transition of CuV2S4 accompanied by a tetragonal distortion which may be understood as a result of lowering of interaction dimensionality inherent to the corner-sharing tetrahedral lattice. 相似文献
213.
A three-dimensional (3D) reconstruction of icosahedral virus is carried out by the icosahedral symmetry-adapted function (ISAF) method in spherical coordinates. In order to reduce the influence of noise, it is better to use the basis functions that have identical symmetry with the object reconstructed. It is verified that the ISAF method has stronger ability to reduce the influence of noise to grain the resolution better than that of the conventional method by the simulation of 3D reconstruction. 相似文献
214.
Jong Hyun Bae 《Applied Surface Science》2007,253(9):4150-4155
Surface functionalization of single-walled carbon nanotube was carried out by introducing ylides groups containing anchored phenol structures. The functionalized nanotube is characterized using elemental analysis, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, Raman spectroscopy and zeta potential measurements. Elemental and FT-IR analysis reveal the successful functionalization of azomethine ylides. Raman spectroscopic studies corroborates that the surface functionalization does not affect the basic crystal domain size of the nanotubes. Functionalized carbon nanotubes exhibit higher zeta potential values showing its higher dispersant ability in water and acetone solvent in comparison to pure carbon nanotube. 相似文献
215.
J.B. Fouet P. Sindzingre C. Lhuillier 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):241-254
We have investigated the quantum J
1
-
J
2
-
J
3
model on the honeycomb lattice with exact diagonalizations and linear spin-wave calculations for selected values of J
2
/
J
1
, J
3
/
J
1
and antiferromagnetic (J
1
> 0) or ferromagnetic (J
1
< 0) nearest neighbor interactions. We found a variety of quantum effects: “order by disorder" selection of a Néel ordered ground-state,
good candidates for non-classical ground-states with dimer long range order or spin-liquid like. The purely antiferromagnetic
Heisenberg model is confirmed to be Néel ordered. Comparing these results with those observed on the square and triangular
lattices, we enumerate some conjectures on the nature of the quantum phases in the isotropic models.
Received 17 November 2000 and Received in final form 21 January 2001 相似文献
216.
Jacob Yunger 《Physica A》2007,386(2):791-798
From extensive biophysical studies of protein folding, two competing mechanisms emerged: hydrophobic collapse and the framework model. Our protein of choice is Barstar—a barnase inhibitor. The approximation algorithm we used to study Barstar folding trajectories is called SDEL—stochastic difference equation in length. Using the native structure as the final boundary value and a collection of unfolded structures as the varying initial boundary value, SDEL calculates an ensemble of least action pathways between these boundaries. The results are atomically detailed folding pathways, with as many intermediate structures as you request in the input. We generated 12 pathways, starting from a structurally wide selection of unfolded conformations. Using the protein's radius of gyration as our primary reaction coordinate, we tracked H-bonds, dihedral angles, native and non-native contacts, and energy along the folding pathways. This paper will follow our findings, with special emphasis on pinpointing hydrophobic collapse as a more appropriate mechanism for Barstar. Comparison with pathway predictions for Barstar using experimental techniques will also be discussed. 相似文献
217.
S.M. Podgornykh S.V. Streltsov V.A. Kazantsev E.I. Shreder 《Journal of magnetism and magnetic materials》2007
We report the results of the investigation of the specific heat of the ferromagnetic Heusler Ni2MnSn, Ni2MnSb, NiMnSb and antiferromagnetic CuMnSb alloys. The low-temperature behaviour of the specific heat may be described as C=γT+βT3 for ferromagnetic compounds and as C=γT+δ T2+βT3 for antiferromagnetic CuMnSb. The values of the density of states from the heat capacity measurements are higher than those from electronic band structure calculations. Debye temperatures are in a good agreement with those obtained from thermal expansion measurements. The Grüneisen parameter is calculated for Ni2MnSn and CuMnSb from the magnetic contribution to the specific heat in the vicinity of TC or TN. 相似文献
218.
D. Gao A. K. Ray 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(1):13-22
Electronic structures of double hexagonal close-packed americium and the
(0001) surface have been studied via full-potential all-electron
density-functional calculations with a mixed APW+lo/LAPW basis. The
electronic and geometric properties of bulk dhcp Am as well as quantum size
effects in the surface energies and the work functions of the dhcp Am (0001)
ultra thin films up to seven layers have been examined at nonmagnetic,
ferromagnetic, and antiferromagnetic configurations with and without spin
orbit coupling. The anti-ferromagnetic state including spin-orbit coupling
is found to be the ground state of dhcp Am with the 5f electrons primarily
localized. Our results show that both magnetic configurations and spin-orbit
coupling play important roles in determining the equilibrium lattice
constant, the bulk modulus as well as the localized feature of 5f electrons
for dhcp Am. Our calculated equilibrium lattice constant and bulk modulus at
the ground state are in good agreement with the experimental values
respectively. The work function of dhcp Am (0001) 7-layer surface at the
ground state is predicted to be 2.90 eV. The surface energy for dhcp Am
(0001) semi-infinite surface energy at the ground state is predicted to be
0.84 J/m2. Quantum size effects are found to be more pronounced in work
functions than in surface energies. 相似文献
219.
P. P. Dholabhai R. Atta-Fynn A. K. Ray 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(3):261-270
Ab initio total energy calculations within the framework of density functional theory have been performed for atomic hydrogen
and oxygen chemisorption on the (0001) surface of double hexagonal packed americium using a full-potential all-electron linearized
augmented plane wave plus local orbitals method. Chemisorption energies were optimized with respect to the distance of the
adatom from the relaxed surface for three adsorption sites, namely top, bridge, and hollow hcp sites, the adlayer structure
corresponding to coverage of a 0.25 monolayer in all cases. Chemisorption energies were computed at the scalar-relativistic
level (no spin-orbit coupling NSOC) and at the fully relativistic level (with spin-orbit coupling SOC). The two-fold bridge
adsorption site was found to be the most stable site for O at both the NSOC and SOC theoretical levels with chemisorption
energies of 8.204 eV and 8.368 eV respectively, while the three-fold hollow hcp adsorption site was found to be the most stable
site for H with chemisorption energies of 3.136 eV at the NSOC level and 3.217 eV at the SOC level. The respective distances
of the H and O adatoms from the surface were found to be 1.196 ?and 1.164 ?. Overall our calculations indicate that chemisorption
energies in cases with SOC are slightly more stable than the cases with NSOC in the 0.049–0.238 eV range. The work functions
and net magnetic moments respectively increased and decreased in all cases compared with the corresponding quantities of bare
dhcp Am (0001) surface. The partial charges inside the muffin-tins, difference charge density distributions, and the local
density of states have been used to analyze the Am-adatom bond interactions in detail. The implications of chemisorption on
Am 5f electron localization-delocalization are also discussed. 相似文献
220.
Y.L. Tang D.J. Branagan D.J. Miller M.J. Kramer R.W. McCallum 《Applied Physics A: Materials Science & Processing》2003,76(6):987-989
The microstructures of nanophase Pr-Co-C-(Ti) materials, which have improved magnetic properties, were investigated by means
of transmission electron microscopy (TEM) to reveal their phase assemblage and grain-boundary structure. The phase assemblage
was carefully controlled by the introduction of TiC nanoparticles and annealing. The optimal nanostructure contained uniformly
distributed PrCo5 and PrCo2 nanophases without any magnetically soft phases, resulting in high coercivity and the characteristics of a single, hard magnetic
phase. TEM analysis confirmed the presence of an amorphous grain-boundary phase surrounding the grains in alloys without TiC.
In contrast, alloys with added TiC showed no amorphous phase and also showed higher coercivity compared to Co-Pr-C. Therefore,
the variation of the grain boundary phases may be effective in changing the degree of exchange coupling. Controlling the formation
of a uniform nanoscale microstructure, leading to improved magnetic properties, is discussed.
Received: 5 September 2002 / Accepted: 10 September 2002 / Published online: 22 January 2003
RID="*"
ID="*"Corresponding author. Fax: +1-630/252-7777, E-mail: ytang@anl.gov 相似文献